Leukocyte infiltration is a basic component of retinal diseases that are leading causes of blindness. These include uveitis, endophthalmitis, and many ostensible clinically non-inflammatory diseases such as diabetic retinopathy, macular degeneration, and proliferative vitreoretinopathy. The initiating insult may vary, but leukocyte elicitation and activation in these diseases involves a common pathway in which leukocyte migrate along and are activated by gradients of potent chemotaxies and cell surface adhesion molecules (CAMs) expressed by resident cells in diseased tissue. The two most active and best characterized leukocyte chemotaxies are IL-8 and MCP-1, two chemokines that are secreted by human RPE cells in response to soluble pro-inflammatory cytokines (e.g., IL-1 and TNF) and other soluble mediators that may be present in the ambient environment. Although RPE cells are known to be involved in many retinal diseases, a mechanism for the initiation of local chemokine production by RPE cells in the absence of ambient pro-inflammatory mediators has not been described. It is hypothesized: (1) that a novel leukocyte-RPE binding mechanism results in high levels of RPE IL-8 and MCP-1 gene expression and protein secretion; (2) that this binding is dependent upon CAMs; (3) that this binding occurs preferentially along the RPE basolateral membrane; (4) that intracellular RPE pathways involved in CAM-dependent leukocyte binding-induced RPE IL-8 and MCP-1 production utilize mediators which also participate in pro-inflammatory cytokine elicitation of these chemokine; (5) that CAM-dependent leukocyte-RPE binding-induced IL-8 and MCP-1 secretion is potentiated by serum proteins and pro-inflammatory cytokines, modulated by growth factors, and inhibited by anti-inflammatory cytokines and drugs, all of which affect the CAMs and/or intracellular pathways mediating RPE responses to leukocyte binding. This project will use a newly developed, polarized human RPE cell culture system to illuminate and characterize how leukocyte-RPE binding at sites of tissue disruption at the blood-retinal barrier may lead to local chemokine production, leukocyte recruitment, and pro-inflammatory cytokine elaboration in a cascading response that correlates with evolving clinical disease.